"Don't we need" may come off as you passive aggressively telling your boss to do it in the same way a spouse may say to their partner, "Don't we need to take out the trash?" as a way to tell that partner to take out the trash. If you are going to put the question, be clear about who it is would update the chart? Also, don't pose the question as a negative "don't" but a positive "do," or an even softer "should."
"I have updated the data in chart A. Should [name] update the data in chart
Be specific about who will have the responsibility of updating the data in chart B, whether it be you, IT, the secretary, or even your boss. Although, I must warn, most bosses do not like it when subordinates try to delegate tasks upwardly to them.